This invention relates to a concrete filled steel tube column and the method of constructing the same, the concrete filled steel tube column constituting, for example, a part of a building structure such as a column and a pile.
A conventional concrete filled steel tube column is a structural column made of a steel tube having a concrete core within it. In this type of column, it is expected that the steel tube enhances the concrete core in axial compressive strength by its lateral confinement.
The above-mentioned type of steel tube column is constructed by carrying out following steps:
First, a steel tube piece is erected at a construction site;
Second, beams are joined to the erected tube piece at a predetermined level;
Third, concrete is charged into the tube piece to form a core within the tube piece;
After the charged concrete is cured, another tube piece is concentrically joined to the upper end of the tube piece having the core in it; and
Thereafter, the fore-mentioned steps are repeated in the same order.
In a column constructed according to the above steps, the tube pieces, which are joined in series, i.e., a steel tube is bonded to the concrete core. Therefore, the steel tube and the core move in singular alignment when axial compression is applied to the column. When the concrete column is subjected to an axial compression beyond a predetermined compressive strength, excess strains develop in the steel tube and the concrete core, resulting in a local buckling in the steel tube or in that the steel tube reaches an yield area under Mieses's yield condition. Thus, the steel tube does not provide the concrete core with sufficient confinement even though the steel tube still has enough circumferential tensile strength, which causes the concrete core to reach a downward directed area of the stress-strain curve at a load applied considerably lower than a predetermined load. For this reason, it cannot be expected to efficiently enhance the concrete core in compressive strength by the lateral confinement of the steel tube hence, a relatively large cross-sectional area must be given to the concrete filled steel tube column to provide sufficient strength for it.